Sometimes our nervous enthusiasm helps us pull the trigger when we should really be holstering that thing. I’ve done it a bunch of times. The best antidote would be to keep in mind what you’re paying for these mistakes we'll occasionally make.
You have to work on paying what you most likely be able to sell it for- just in case it starts to suck fast like the last thing you made a mistake on.
Or, if you pay a little more and take a little bit of a beating when you unload it, at least it’s just a little bit of a beating.